From ancient times to the present, human beings are very yearning for immortality, the adult worm of caenorhabditis elegans is only one millimeter, they not only have hermaphrodite forms, but also have a very short life cycle, so we choose to use nematodes to study aging. By chemical mutagenesis to produce genetic mutations, we found that mutated bugs can significantly extend their lifespan, and at the same time, dieting appropriately can also effectively prevent aging. What are the advantages of using nematodes to study aging? How do we use nematodes to study metabolism?
Produced by: Gezhi Dao Pulpit
The following is the transcript of Professor Liu Ying's speech at the Institute of Molecular Medicine of Peking University:
Hello everyone, my name is Liu Ying, from the Institute of Molecular Medicine of Peking University, mainly engaged in research in the field of life sciences. The topic I want to share with you today is called small bugs solving big problems.
A person's life will go through a series of stages of birth, old age, illness and death. Throughout our life cycle, there are many important life sciences issues that are very complex.
But for me, I'm concerned with two issues, aging and metabolism. Everyone may think that this is a very big scientific problem, but in our laboratory, we are just using small bugs to study the big problem of human life, old age, illness and death.
Today I want to share with you how we use these small bugs called nematodes to study aging and metabolism.
Why should I study aging? Since ancient times, from the East to the West, human beings have always had a tireless yearning and pursuit of immortality. In ancient Times, there was such a mythical story in China, Chang'e stole the elixir that her husband wanted from the Queen Mother of the West, so there was the story of Chang'e running to the moon.
The same legend is also said in the West, the name of the picture below is Called The Fountain of Youth, and the Chinese name is the Fountain of Youth.
The painting depicts a spring that you can think of as a fountain of life. A yellow leaf, after falling into this spring, can turn green again; or a dying insect, falling into this spring, can fly immediately; if we humans, especially the elderly, go to this spring to bathe, we can immediately return to old age. There was an explorer in Spain who, because he wanted to find the Fountain of Youth, began his own sailing trips and expeditions, and eventually it is said that he discovered the Fountain of Youth in Florida, USA.
Therefore, we human beings have always longed for immortality.
As I was about to graduate from my PhD, I began to wonder, what am I going to study in the future? At that time, I began to be interested in aging, and I wondered why humans are aging. Is there any way to delay aging?
<h1 class="pgc-h-arrow-right" data-track="14" > Why choose nematodes to study aging? </h1>
Our laboratory will use some model organisms for scientific research, and the following figure shows the more common model organisms in the life sciences field. As you can see, from left to right, there are bacteria, yeast, and we commonly use nematodes, fruit flies, zebrafish, mice, and monkeys.
My research group mainly uses nematodes to study aging, why choose nematodes?
Let me first briefly introduce the nematodes, the scientific name of the nematodes is relatively long, called caenorhabditis elegans. Nematodes are widely distributed in nature, and even in outdoor soils, we are able to isolate nematodes.
But you must not think that nematodes are the kind of crawling, squirming, and very disgusting little bugs. In fact, they are very small, and the adult worms of the nematodes are only about one millimeter. We often need to use a microscope to observe the nematodes.
The image above is the morphology of the nematodes that we see under the microscope. It can be seen that it has two forms, the larger form is hermaphrodite, and the smaller form is male worm. In nature, hermaphrodite nematodes account for the vast majority, and probably more than 98% of bugs exist in a hermaphrodite manner.
Nematodes are very well cultivated in the laboratory, and we generally use round plastic Petri dishes with a diameter of a few centimeters to more than ten centimeters.
When cultivating, you need to first lay a layer of agar in the Petri dish, and then lay a layer of bacteria on top of the agar to grow nematodes. Because nematodes feed on bacteria, the presence of agar can provide both nematodes and bacteria with some of the nutrients they need. The small Petri dishes in our laboratory are the growing environment of the nematodes.
Why did I choose nematodes to study aging? The most critical reason is that their life cycle is very short.
We can see from the figure below that when the nematode hatches from the egg, it will pass through four larval stages, which can be named L1, L2, L3 and L4 respectively. It then turns into a fertile adult worm, and it usually takes about two to three days for the nematode to lay eggs.
After the end of the spawning period of nematodes, adult nematodes slowly enter the aging phase until they die. Under the microscope, we can observe the eggs of nematodes, the larvae one by one, and every time the nematodes enter the previous larval stage into the latter larval stage, it will complete a molting, then become larger, and finally enter the adult stage.
In the laboratory, the temperature of the nematode culture environment is different, and their lifespan is also different. For example, if we grow nematodes in a 20-degree Celsius culture environment, their life cycle is about 20 days.
If you want to know whether an experimental condition can delay the aging of nematodes, it may take more than a month to obtain experimental results. But if a similar experiment were to be done to study mice, it would take two to three years to get the results of one experiment.
Among the commonly used model organisms, the nematode is in the middle of evolution, it is not as low as bacteria and yeast, it will also go through its own development, growth, reproduction and aging processes. So we use nematodes as models of aging.
As you can see from the video above, observe a bug under the microscope, and take pictures of the bug under the microscope every day to observe its state.
Each stage of the bug has a pronounced state manifestation. For example, after the end of the spawning period, the adult bug will begin to age. When it ages, its exercise is significantly slower, it does not move much, and its eating is also significantly reduced.
After the insect enters the adult stage, we take a picture of it every day, arrange the photos of its youth and the photos of its old age from top to bottom, and we can find a very obvious phenomenon, the old worm is significantly shortened, its height has become shorter, and the skin has also appeared wrinkles, including its internal intestines and other tissue structures, which have also undergone tremendous changes.
The aging of nematodes is similar to that of humans in many forms. Therefore, we feel that with the help of nematodes to do aging research, the research results obtained may be able to be applied to higher organisms.
<h1 class="pgc-h-arrow-right" data-track="32" how to use nematodes to study aging >? </h1>
How do we use nematodes to study aging? We are here with the help of the form of a genetic mutation. As everyone should know, genes refer to a piece of DNA sequence that carries genetic information, and gene mutations often occur in nature in the process of evolution.
For example, we can see that the background of the following figure is off-white, which is a tree trunk of gray and white color. If you look closely, there is also a moth lying on this trunk, which is a very common moth in Britain. Because the color of the moth itself is very close to the color of the trunk, it can avoid being discovered by its own natural enemies and avoid being preyed upon.
However, with the development of the British Industrial Revolution, environmental pollution is serious, the trunk is polluted from gray to black, and when this white moth lies on the black trunk, they are easily found and eaten by predators, which is very unfavorable for the survival of moths.
Some moths produce genetic mutations that cause the genes that control the color of their bodies to change, making them change from white to black.
You can see from the picture above that there is a black moth on the left side of the picture. Because of the mutation of this gene, its color is once again close to the color of this trunk, and the protective color is reproduced. So for moths, this genetic mutation is advantageous for it.
Because in nature, the frequency of mutations in this gene is very low. So in the laboratory, we often use chemical reagents to treat small bugs and increase their mutation frequency, which is called chemical mutagenesis.
At this time, I remembered a cartoon I often watched when I was a child called "Teenage Mutant Ninja Turtles", these four Teenage Mutants themselves are the product of genetic mutations, and genetic mutations make them have superpowers.
In fact, in the experiment, we hope to find some nematodes with superpowers, what are the superpowers we pay attention to? It is a superpower that can delay aging and prolong the life of nematodes. By chemical mutagenesis, scientists have indeed found that mutated bugs can significantly extend their lifespan.
The image above is the life curve of the nematode, the abscissa is the date of the growth of the nematode, that is, the number of days, and the ordinate coordinate refers to the approximately how many percent of the bugs are still alive in a Petri dish.
As you can see, the curve composed of each small white box is the life curve of a wild-type nematode that grows normally in the wild. In the first few days, 100 percent of the nematodes were alive. Over time, some nematodes began to die. By about 20 days, only about 50 percent of the nematodes are still alive. By about 30 days, basically all the nematodes were dead.
But scientists screened and found a bug with a genetic mutation called daf-2.
This curve of the black box is the growth curve of the mutant insects. It can be seen that the lifespan of this insect has been significantly extended. It wasn't until about 80 days that the bugs all died, and their lifespan was extended to 2.5 times.
In addition to the daf-2 gene, scientists have actually screened for some other genes.
For example, one of these genes is called eat-2. The white box shown in the figure below is still the growth curve of normal wild-type insects, and the other four groups are with EAT-2 gene mutations, and it can be clearly seen from the figure that the mutations in the eAT-2 gene in the growth curves of the four mutant nematodes also extend the lifespan of nematodes like the daf-2 gene.
The word eat is actually the meaning of "eat" in our Chinese words. What are the consequences of a mutation in the eat-2 gene? It is that the nematodes eat less, indirectly simulating a calorie-restrictive diet, in layman's terms, proper dieting.
So this finding on nematodes tells us that perhaps dieting properly, or calorie-restrictive eating, can extend the lifespan of a species.
Are the findings on nematodes applicable to higher organisms? Another group of scientists conducted experiments on monkeys. If you first see the two monkeys in the picture above, I think your first impression may be the same as mine, and you will think that the monkey on the right is obviously older than the monkey on the left.
But their age is actually similar, the monkey on the left is 25 years old, the monkey on the right is 26 years old, and their main difference is that the monkey on the left eats about half of the daily food intake, which is about half of the monkey on the right, that is to say, it is carrying out a calorie-restrictive diet.
So from the results of this experiment, we can see that higher organisms can also prolong their life by dieting moderately.
<h1 class="pgc-h-arrow-right" data-track="52" > use nematodes to study metabolism</h1>
We are now talking about diet, diet is closely related to the metabolism of the body, how can we use nematodes to study metabolism?
I myself am very concerned about metabolism, and I am also curious about how we feel the presence of these nutrients when we ingest food and these nutrients enter our bodies. How do we activate our anabolics and store these nutrients in case we need them?
How the body feels hungry when everyone is hungry, so as to start the catabolism. For example, how do these processes, such as breaking down fat to provide energy to the body?
In my own research group, we still use this little bug for our research. Because nematodes can feel their hunger very intelligently and begin to break down the fat stored in their bodies.
We use a dye in the laboratory called oil red O to stain the fat of nematodes.
The group of nematodes on the left of the figure above are normally fed nematodes, and its fat staining, that is, the red color is relatively dark, indicating that it has a large amount of fat stored in its body at this time. If I starve the bug for 12 hours, it becomes the group of bugs on the right, indicating that it knows it is hungry at this time, and it starts to decompose its own fat, and the red part of the stain becomes lighter.
We can see the gene expression levels of these hungry bugs from the graph below. The increased expression of these genes associated with lipolysis indicates that these genes are beginning to function and begin to promote lipolysis.
We use nematodes to conduct our research, mainly relying on its two research advantages. One of the advantages is that we can easily make transgenic nematodes through a technique called microscopic injection.
As shown in the picture above, we fixed the little bug, stuck a very thin glass needle into the worm, and kept the tip of the needle into its reproductive glands. At this time, from the other end of the needle, a specific DNA is injected, so that the next generation produced by this bug can express the gene.
Another research advantage of nematodes is that these bugs are transparent throughout, and we can observe them directly under the microscope. For example, we can see directly under the microscope how each cell division occurs.
By studying the two advantages of nematodes, our research group established genetically modified insects that study lipolysis. In simple terms, we connect the gene that promotes lipolysis to a green fluorescent protein. When the bug is hungry, it needs to promote lipolysis, at which time it will upregulate the expression of lipolysis genes, and the corresponding green fluorescent protein will be expressed at the same time.
The group of bugs on the left in the figure below, that is, the bugs that are normally fed, the green fluorescence will not be expressed and will not be brightened. But if you starve these bugs for 12 hours, it needs to break down fat, so the green fluorescence is also produced, and under the microscope we can see that these bugs are brightened.
So we can still use these transgenic bugs to study the genetic mutations caused by chemical mutagenesis, or use gene knockdown to observe which genes are mutated or missing.
Even when small bugs eat normally, they can initiate the process of lipolysis. Through such research, we have now discovered a gene called HLH-11. When the gene in the nematodes is knocked out, you can see that in the nematodes, all the genes equivalent to controlling lipolysis have become higher expression levels, and they have become red in the following figure. Red indicates that its expression is higher.
In addition, we can also directly monitor the content of each fat molecule in the nematodes through technical means.
As you can see, each of the dots on the graph below represents the molecule of each fat. For the gene-knocked bug, all the dots are shifted to the left, indicating that all of its fat content is decreasing.
At the same time, we also found that our research is indeed applicable to higher organisms, because there are also homologous genes in higher organisms that perform the same function as nematodes. So we cultured our people's liver cells outside the body, and also knocked out the gene we found.
In the figure below, on the left are normal human liver cells, and if I stain the fat with oil red O, I can see the presence of lipid droplets in these cells, which proves that these cells have a large amount of fat accumulation. But when I knocked out the gene I found, it became the group of cells on the right side of the picture below, and I basically couldn't see the presence of fat droplets, and the fat inside these cells had been broken down.
If we can upregulate the decomposition of fat in these ways in the future, is it possible that we can activate our own lipolysis while we eat normally? If it can be achieved, I think maybe human weight loss will no longer be a problem. Thank you!
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